A valve, just as any hydraulic device for the regular or occasional outlet or distribution of fluid, comprises a blocking element which is caused to open by means of an overpressure of the fluid or by means of an external operating device.
In a clack-valve, when the pressure does not exceed a value which is considered to be normal, the clack-valve blocks the outlet orifice, this being caused by the thrust of a loaded spring. The pressure rise causes the clack-valve to open either rapidly or gradually, which generates a rapid pressure drop upon discharge.
When the overpressure remains low, the clack-valve is inclined to close again after opening due to the pressure drop occurring when the clack-valve opens.
Provided conditions remain identical, the closing of the clack-valve is followed by an increase in pressure, thus causing the clack-valve to open again, and so forth.
As this phenomenon is not cumulative, it causes alternating movements called clatter.
Depending upon the magnitude of the pressures, the frequency of this clatter may increase and may cause repeated shocks of the clack-valve on its seat and overheating, which in turn may cause damage, such damage being the source of valve malfunction, leaks and even jamming in the open position, and possibly leading to eventual failure of the controls.
Such malfunctions may cause severe damage to the installation and to the whole environment. Damping devices are known which make it possible to avoid or at least to sufficiently reduce the clatter movement of the valves.
Such mechanical devices simply make it possible to neutralize the phenomenon of clack-valve clatter.
Another group of several damping devices are provided with stabilizers or hydraulic brakes. Examples can be found in French Patent Nos. 2.473.670 in the name of Electricite de France and 2.484.582 in the name of the Fisher Controls Company.
French Patent No. 2.473.670 relates to a safety valve comprising a hydraulic damping device between the clack-valve and the spring, the plate-type piston of the damping device being inserted between the spindle of the clock-valve and the spindle of the spring. The piston demarcates two chambers, one on either face, the said chambers being interconnected by means of one or several simple connection(s) in the form of flexible or rigid conduits.
By way of variation, a communication between the chambers is moreover provided, this communication being effected through calibrated transverse passages, each of which may be provided with a clack-valve, in order to obtain a different damping effect of the movable components of the valve during opening and closing, by calibrating these passages differently.
This damping device can unfortunately not function correctly due to its lack of thermal compensation.
Moreover, the damping device being placed invertedly between the clack-valve and the spring, causes serious complications during assembly. Moreover, there exists no visual referece by means of which leaks and the lack of oil due to such leaks may be observed.
French Patent No. 2.484.582 relates to an hydraulic auxiliary device with a stabilizer in the form of a cylinder, mounted vertically on the top of the valve. In this cylinder is a moving piston which is connected to a spindle. The upper portion of this spindle is integral with a rigid external frame which opens out vertically around the cylinder in order to ensure the connection between the piston spindle and the extension of the valve spindle. A transverse plate provided with orifices blocks the internal chamber of the cylinder at a certain height. In the upper part this plate demarcates the course of the piston and forms two chambers inside the cylinder, these two chambers being interconnected through a distribution block. The communication is effected inside the distribution block by means of a first channel provided with a variable-section restriction followed by a second channel occupied by a non-return ball-valve through which the fluid passes in the direction from the upper chamber to the lower chamber.
The oil level may be checked by means of sight slits screwed onto the cylinder cover.
By driving back the oil from one chamber to the other through small orifices, the stabilizer according to this invention makes it possible to regulate the displacement of the movable components of the valve, thus eliminating the sudden accelerations and decelerations which may generate the clatter movements.
Stabilization, however, even though it is probably quite efficient, necessitates the construction of an external frame for transmitting the movement, which complicates the construction. Moreover, as the oil does not fill the chambers completely, a closed circuit is not formed. Consequently, use in an upright position is imperative.
In these devices neither compensation for the volume of oil lost due to leaks or temperature variations, nor improved efficiency is provided.
It is known elsewhere to compensate for the oil volume by means of a capsule or bellows filled with a gaseous fluid which is susceptible to contractions or expansions.
French Patent Nos. 2.381.343 and 2.408.771 QUIRI relate to one or several gas-filled volumes which are susceptible to dimensional variations, these volumes being placed in the hydraulic circuit of a damping device in order to compensate for expansions and to absorb pressure shocks.
The main object of these inventions is twofold. On the one hand they relate to compensation for volume variation(s) due to the expansion of the oil resulting from a rise in temperature, and on the other hand they relate to the suppression of the cavitation phenomenon by compensating for losses in the oil charge due to the passage thereof through the discharge nozzles at the time of aspiration.
In order to suppress or at least greatly reduce the clatter of a valve without disturbing the functioning of the valve, the damping must be progressive and efficient.
Moreover, to ensure reliable functioning, it is desirable to be able to compensate automatically for losses and to check the oil level quickly.
Finally, the reliability required dictates the necessity for the valve to open rapidly and to close gradually.